The use of therapeutic gases to treat a human or animal patient has been known in the art for many years. A number of different gases may be added to a respiratory gas that is inhaled by a spontaneously breathing, non-ventilated patient. These gases may be used to achieve some therapeutic effect, service a diagnostic function or have some other desirable purpose. Such gases will be referred to herein as “therapeutic gases.” One skilled in the delivery of therapeutic gas will understand that the disclosure can be used to teach either human or animal patients. Accordingly, no limitation to human is intended by references to patient in this disclosure.
One therapeutic gas is nitric oxide (NO), which is administered by inhalation in low concentrations to treat primary or secondary pulmonary hypertension or other diseases. In many cases, nitric oxide or other therapeutic gases come from a high concentration source such as a high concentration compressed gas cylinder. The gas source may be pure or may contain some concentration of therapeutic gas in a carrier gas. There may also be cases where more than one therapeutic gas is used, with or without a carrier gas or gases. It is often necessary to dilute therapeutic gas to a lower concentration and mix it with air and/or oxygen prior to delivery to the patient. This dilution may be necessary to achieve a desired dosage concentration and/or to avoid or reduce adverse bioeffects that may occur if high concentration gas is delivered to the patient. If the therapeutic/carrier gas is not sufficiently oxygenated, it is necessary to mix it with air prior to delivery to the patient. In some cases, it is necessary to add supplemental oxygen to the mixture to avoid a hypoxic respiratory mixture or to enrich the oxygen content of the respiratory gas above twenty-one percent. In the latter case, the oxygen will also be considered as a therapeutic gas.
NO is one of a number of therapeutic gases that are administered to a patient and require dilution from a high concentration form to a lower, safer concentration before administration to a patient. NO will be the primary focus of this disclosure; however, one skilled in the surgical arts will understand that the disclosure can be used to teach other gases as well. Accordingly, no limitation to NO is intended by the references to NO in this description.
The art contains several devices and systems to deliver therapeutic gas to a spontaneously breathing, non-ventilated patient. However, as will be discussed, each of the known systems and devices has drawbacks.
A system that has continuous flow to a mask is one such known system. A therapeutic gas, oxygen and air are supplied from sources such as compressed gas cylinders or a hospital wall. A continuous flow of these gases is titrated together before delivery to a patient. The flow rate of each gas is set to achieve the desired concentration of the therapeutic gas and oxygen in the respiratory gas. The total flow rate is set greater than the peak inspiratory flow rate. If a reservoir bag is added to the inspiratory portion of the overall circuit, then the total flow can be reduced, but must still be greater than the minute volume of the patient. The mixed gas is connected into the mask, from which the patient inhales. Exhaled gas and excess inhalation gas flow from an outlet side of the mask and may be scavenged. This system has the disadvantage of wasting gas since not all therapeutic gas is inhaled by the patient. Scavenging is required to prevent the therapeutic gas from entering the environment. In addition, large volumes of air and/or oxygen must be supplied to dilute/mix the therapeutic gas. Also, therapeutic gas is delivered to the entire respiratory tract, not just the areas where it is needed. This may increase adverse bioeffects and the possibility of undesirable reaction products from the therapeutic gas. The mask also makes eating and talking difficult and is also aesthetically unappealing. Still further, a mask may make some patients nervous and cause anxiety by making them feel confined.
Yet another system uses a bolus pulse of therapeutic gas to, a mask. In this system, therapeutic gas is delivered to the patient as a bolus of gas that is delivered via the mask. The bolus of therapeutic gas is delivered over a short period of time and is not significantly diluted by inhaled air or supplemental oxygen. Supplemental oxygen may also be delivered via the mask. The patient's breathing waveform is monitored and the bolus of therapeutic gas is delivered to the mask intermittently, in synchronization with the respiratory waveform so,that the therapeutic gas is inhaled at a set phase of the respiratory waveform. The bolus is preceded and/or followed into the respiratory tract by air/oxygen. This system and method has the disadvantage that it does not dilute the therapeutic gas, so a high concentration source cannot be used. In addition, the short duration of the bolus means that a higher concentration of therapeutic gas is required to deliver the same number of molecules of the gas to the patient. This could have adverse bioeffects. This method does not have the flexibility of varying *the concentration of the therapeutic gas at various times during inspiration. The mask has the same drawbacks as heretofore discussed.
Yet another system and method uses an undiluted pulse via a nasal cannula. A nasal cannula is a device that can be used to transmit therapeutic gas from one or more therapeutic gas sources to the nose of a patient for inhalation. It includes one or more connectors at one end of the device to connect to one or more therapeutic gas sources, one or more long lumens to transmit the gas, and nasal prongs at the other end to inject one or more therapeutic gases into the patient's nose. The word “lumen” will be used in this disclosure to represent a long, narrow, flexible fluid conduit that is less than 0.8 cm in internal diameter. A nasal cannula is typically much less obtrusive than a mask and allows the patient to talk and eat while receiving gas therapy. In the method of undiluted pulse delivery via a nasal cannula, therapeutic gas is delivered via a nasal cannula as an intermittent flow pulse during inspiration. Air pressure in the nares drops at the start of inspiration. This pressure drop is transmitted through the cannula and is detected in the pulse delivery device. Therapeutic gas flow is turned on for a period of time during inspiration. The therapeutic gas flows directly into the nares from the cannula. While overcoming many disadvantages associated with a mask, this method also has disadvantages as practiced in the known art. For example, the therapeutic gas is not diluted prior to entering the nares in many known systems. If a high concentration source is used, high concentration gas may contact the tissues before it is diluted in the respiratory tract. This may have adverse bioeffects. If lower concentration gas is used, the source lifetime/size advantages of a high concentration source are lost. Also, the final dilution concentration in the respiratory tract is limited. It is lower for any given volume of therapeutic/carrier gas, and this volume must be limited to avoid a hypoxic respiratory gas mixture. Still further disadvantages will be discussed below in reference to the use of known cannulas.
Still another known method and system for administering therapeutic gas to a patient includes an undiluted pulse via a nasal cannula and oxygen via another lumen. In this method, gas may be delivered as discussed above, with the addition of supplemental oxygen delivered via a second lumen in a dual lumen cannula. This method has all the disadvantages discussed above, except that it allows a higher diluted concentration to be delivered to the respiratory tract without having a hypoxic mixture. This has the accompanying disadvantage of requiring a supplemental oxygen source.
A diluted pulse to a cannula can also be used. In this method, the therapeutic gas may be delivered by a nasal cannula and diluted prior to entering the nares. This can be done by mixing it with a diluent gas from a diluent gas source before it leaves the cannula. The therapeutic gas concentration can be reduced to a safe level prior to entering the nares. It is further diluted in the respiratory tract by entrained air from the room. This method has the disadvantage of requiring a diluent gas source. If supplemental oxygen therapy is desired, oxygen or enriched air may be used as the diluent gas, but it is more difficult to control the oxygen concentration reaching the respiratory tract because a minimum diluent gas flow is required to dilute the therapeutic gas to a safe concentration in the cannula.
Still another known method includes a continuous flow of therapeutic gas and supplemental oxygen delivered to the patient via a nasal cannula. This method has therapeutic gas delivered continuously via a nasal cannula by titrating the therapeutic gas with air and/or oxygen before the cannula or in the cannula before it reaches the flares. The therapeutic gas concentration can be reduced to a safe level prior to entering the nares. It is further diluted in the respiratory tract by entrained air from the room, This method has the disadvantage of requiring a diluent gas source. If supplemental oxygen is required, a source of air and a source of oxygen will be required or it will be difficult to control the oxygen concentration reaching the respiratory tract.
Yet another known method of administering therapeutic gas to a patient includes use of a transtracheal catheter. In this method, therapeutic gas can be delivered directly to the trachea of the patient via a transtracheal catheter. Therapeutic gas, flow might be continuous or pulsed. This method has the disadvantage that the therapeutic gas is not diluted prior to entering the respiratory tract. If a high concentration source is used, high concentration gas may contact the tissues before it is diluted in the respiratory tract. This may have adverse bioeffects. If lower concentration gas is used, the source lifetime/size advantages of a high concentration source are lost. Also, the final diluted concentration in the respiratory tract is limited. It is lower for any given volume of therapeutic/carrier gas and this volume must be limited to avoid a hypoxic respiratory gas mixture. The transtracheal catheter is invasive, which is often undesirable.
The art has also developed methods which deliver therapeutic gas to a patient during certain times. In such systems, gas delivery is pulsed on during inspiration. Other systems also include means for adjusting dosages, durations, flow rates and the like.
It is noted that not every patient has the same breathing pattern as other patients so a pulse configuration and time that is suitable for one patient may not be completely efficient for another patient. The shape of the gas pulse (flow rate versus time profile) of a first gas may be an approximately arbitrary shape. Some devices for pulsed gas delivery to spontaneously breathing patients use a pulse of a set flow rate and vary the duration of the pulse to change the dosage of gas to a patient. This results in an approximately rectangular flow versus time shape of the pulse. Other devices use a constant pulse duration but flow rate is altered to change dosage. Flow rate is constant during any single pulse and the pulse shape is approximately rectangular.
There is a need for a system that is adaptable to customizing the pulse shape, can easily adjust the dose, is adaptable to various conditions and modes of operation for various patients having individual requirements and is easily maintained by various caregivers.
Still further, some patients require delivery of more than one therapeutic gas. Therefore, there is a need for a system that is amenable to delivering more than one therapeutic gas to a patient if necessary.
Since many patients have individual requirements, it is necessary that a therapeutic gas delivery system be amenable to use by a variety of caregivers ranging in expertise from professional nurses and doctors to laymen in a home environment. In order to be most efficient and effective, the system should efficiently deliver therapeutic gas to the patient at all desired times, even if a primary source of gas is being changed. This may be particularly important in some applications such as nitric oxide therapy where interruption of the therapy can result in a “rebound” effect where patient symptoms become as bad as or worse than they were before the therapy began. To be most versatile, the system should be amenable to use with either a nasal cannula (nasal prongs) or a mask and be easily used, monitored and maintained by a variety of caregivers.
There is thus a need for a system which is amenable to use by a variety of caregivers and which has means for delivering, therapeutic gas in an uninterrupted manner when desired.
More specifically, even though there are several cannulas known in the art, these known cannulas have various drawbacks that may vitiate advantages obtained from customizing a therapeutic gas delivery system in order to overcome the drawbacks associated with known systems.
For example, known cannulas do not have means for efficiently controlling mixing of gases and do not have a gas mixing area that is most efficient or most efficiently located.
Therefore, there is need to improve the cannulas now used in connection with therapeutic gas administering systems.
More specifically, many known cannulas do not provide a location for mixing gases that is remote from a patient's nares. Such a remote mixing location can be advantageous for better control of the final mixture administered to the patient. Such a remote location can also be controlled without inhibiting a patient in any way. However, since known cannulas do not have such an element, they have disadvantages.
Still further, many known cannulas have designs that waste therapeutic gas. Further, many known cannulas cannot be used in a system that can precisely detect breathing patterns of a patient and cannot be used to precisely and accurately control dosage, concentration and flow rates of the gases.
Therefore, there is a need for a cannula that efficiently administers therapeutic gas to a patient in a manner that overcomes the drawbacks of known cannulas.
Still further, many systems that are used to administer therapeutic gas to a patient include primary gas sources in the form of pressurized cylinders. Some of these systems include a “flow direction” check valve downstream of the inlet to seal the system when the supply pressure is removed. However, a check valve system may have drawbacks if used in certain circumstances.
For example, when a pressurized source is exchanged, there exists the possibility that air will be trapped within the volume Of the system plumbing that is exposed to air during the exchange. It is desirable to keep that volume of air as small as possible so the resulting trapped air volume is reduced. Any trapped air will degrade the quality of the high purity gases contained within the remainder of the system when intervening valves are opened. This degradation is proportional to the volume of trapped air. Therefore, it is desirable to maintain this dead volume to a minimum.
Furthermore, it is advantageous to provide a system sealing action as close to the supply inlet as possible to further minimize the dead space volume upstream of the sealing surfaces. A flow direction check valve is not able to achieve all of these goals. Therefore, there is a need for an equalizing valve that can minimize dead space volume.
It is noted that it is possible to flush or purge the system to remove contaminated gas from some dead space regions. However, for purging to be effective, the dead space must be substantially swept out during periods of gas flow. If there are poorly swept regions within the dead space, purging will have to be extended to allow for diffusion and other mechanisms to dilute the contaminated regions. Therefore, there is a need for a means for ensuring proper purging of a system used to administer therapeutic gas to a patient.
Furthermore, purging requirements are strongly dependent on the relative size of the contaminated volumes. Purging is often complicated in many situations due to possible toxic effects of the therapeutic gases; and the high cost of medical grade gases.
Therefore there is a further need for a valve that will make purging most efficient and effective while overcoming the just-mentioned problems.
It is also noted that an autonomous gas delivery system should be able to detect the supply pressure so when a pressurized cylinder has been attached and the supply valve opened, a control system is signaled. This requires suitable positioning of a pressure sensing element.
However, in order to maintain low dead space, a pressure sensor must be located on the downstream side of an inlet sealing mechanism. In the prior art, a simple back flow prevention check valve has provided this function. A check valve will seal when there is a lower supply pressure on the downstream side of the check valve. If the check valve seals, the pressure sensor, which is located further downstream of the check valve, will continue to show the pressure when the check valve is closed and will not indicate the actual supply pressure. If, subsequent to this, a supply is attached that is at a lower pressure than the “checked” pressure, the system will not be able to detect the connection.
Therefore, there is a need for a means for sealing a system such as disclosed herein which will be able to fully detect and control the flow of the system during changing of gas sources.
In general, it is desirable to close off the inlet of a system such as disclosed herein when a supply is detached and to maintain the inside of the high purity system at a positive pressure with respect to atmospheric pressure. By closing off the inlet, the chance of contamination is reduced. By maintaining a positive internal pressure, any small leaks that may be present will tend to leak in an outward fashion helping to prevent atomospheric gas from entering the system.
Therefore, there is a need for a means for connecting the system of the present invention to a source of gas that will reduce the possibility of contamination of the system.